Allowing them to windmill on the ground is actually better for the engines than locking them in the short term
If you lock them then the weight of the shafts will rest on the same point of the bearings and seals and cause warping and damage, particularly the heaviest LPC/LPT N1 shaft.
By rotating it ensures that oil is properly distributed around the engine bearings and any oil seals and keeps the bearings moving which keeps them circular.
Some engine manufacturers will often, whilst transporting engines covered up on low-loaders, attach a low speed electric motor to the engine to rotate the shafts slowly to help protect the bearings and seals.
Last edited by Burnie5204; 17th Jan 2014 at 21:49.